Silicon and silicon germanium nanowire structures

ABSTRACT

Methods of forming microelectronic structures are described. Embodiments of those methods include forming a nanowire device comprising a substrate comprising source/drain structures adjacent to spacers, and nanowire channel structures disposed between the spacers, wherein the nanowire channel structures are vertically stacked above each other.

This is a Continuation of application Ser. No. 14/789,856 filed Jul. 1,2015 which is Divisional of application Ser. No. 14/274,592 filed May 9,2014 now U.S. Pat. No. 9,129,829 issued Sep. 8, 2015 which a Divisionalof application Ser. No. 12/958,179 filed Dec. 1, 2010 now U.S. Pat. No.8,753,942 issued Jun. 17, 2014 which is hereby incorporated byreference.

BACK GROUND

Maintaining mobility improvement and short channel control asmicroelectronic device dimensions scale past the 15 nm node provides achallenge in device fabrication. Nanowires used to fabricate devicesprovide improved short channel control. For example, silicon germanium(Si_(x)Ge_(1-x)) nanowire channel structures (where x<0.5) providemobility enhancement at respectable Eg, which is suitable for use inmany conventional products which utilize higher voltage operation.Furthermore, silicon germanium (Si_(x)Ge_(1-x)) nanowire channels (wherex>0.5) provide mobility enhanced at lower Egs (suitable for low voltageproducts in the mobile/handheld domain, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming certain embodiments, the advantages of thevarious embodiments can be more readily ascertained from the followingdescription of the embodiments when read in conjunction with theaccompanying drawings in which:

FIGS. 1A-1N represent methods of forming structures according toembodiments.

FIGS. 2A-2I represent methods of forming structures according toembodiments.

FIGS. 3A-3G represent methods of forming structures according toembodiments.

FIGS. 4A-4M represent methods of forming structures according toembodiments.

FIGS. 5A-5D represent methods of forming structures according toembodiments.

FIG. 6 represents a system according to embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, the specificembodiments which may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theembodiments. It is to be understood that the various embodiments,although different, are not necessarily mutually exclusive. For example,a particular feature, structure, or characteristic described herein, inconnection with one embodiment, may be implemented within otherembodiments without departing from their spirit and scope. In addition,it is to be understood that the location or arrangement of individualelements within each disclosed embodiment may be modified withoutdeparting from their spirit and scope. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the embodiments is defined only by the appended claims,appropriately interpreted, along with the full range of equivalents towhich the claims are entitled. In the drawings, like numerals refer tothe same or similar functionality throughout the several views.

Methods and associated structures of forming and utilizingmicroelectronic structures, such as nanowire device structures, aredescribed. Those methods and structures may include forming a nanowiredevice comprising a substrate comprising source/drain structurescomprising nanowires between the source/drain structures, wherein thenanowire channel structures are vertically stacked above each other.Various embodiments included herein enable mobility improvement andshort channel control as device dimensions scale past the 15 nm node.Embodiments further enable enhanced isolation of channels from thesubstrate, mitigation of the capacitance associated with spacer-gapseparation, and vertical architecture scaling with nanowires.

FIGS. 1A-1N illustrate embodiments of forming microelectronicstructures, such as forming nanowire device structures, for example.FIG. 1A illustrates a substrate 100. In one embodiment, the substrate100 may comprise a bulk silicon substrate 100. In other embodiments, thesubstrate 100 may comprise a silicon on insulator substrate (SOI) 100,but may also include any type of suitable substrate material. In anembodiment, a first silicon germanium 102 material may be grown byepitaxial growth on the substrate 100. In an embodiment, a first siliconmaterial 104 may be epitaxially grown on the epitaxial first silicongermanium 102. A second layer of silicon germanium 102′ may be formed onthe first silicon layer 102, and a second layer of silicon 104′ may beformed on the second silicon germanium 102′. In another embodiment, thenumbers of alternating epitaxial silicon germanium layers 102/epitaxialsilicon layers 104 formed on the substrate 100 may be varied, dependingupon the particular application. In another embodiment, the layer ordercan be reversed with alternating layers of epitaxial silicon 104 andepitaxial silicon germanium 102 formed on the substrate 100.

In an embodiment, the epitaxial stack 120 of silicongermanium/silicon/silicon germanium/silicon may be patterned usingconventional patterning/etching techniques (FIG. 1B). For example, thestack structure 120 may be etched at a trench etch process, such asduring a shallow trench isolation (STI) process, wherein trenches 101may be formed in the substrate 100 to form fin structures 107. Each ofthe fin structures formed 107 may be separated from each other by anoxide 103 that may be formed in the trenches 101.

In an embodiment, the fin structures 107 may comprise a dual channelportion of a gate all around (GAA) nanowire device. The number ofchannels in the device will depend on the numbers of layers in the finstructures 107. The fin structures 107 may comprise nanowire structures.Spacers 106 may be formed on and across the fin structures 107 and maybe disposed orthogonally with respect to the fin structures 107 (FIG.1C). In an embodiment, the spacers 106 may comprise any material thatmay be selective during process to the fin structure 107 materials.

In an embodiment, a gate electrode material 108 may be formedwithin/between spacers 106, and may be formed around portions of the finstructures 107 located between the spacers 106. In an embodiment thegate electrode material may be formed around portions of the finstructures 107, and the spacers 106 formed on either side of the gate.The gate 108 may comprise polysilicon, in some cases, and may comprise asacrificial gate structure 108. In an embodiment, a portion of the finstructure 107 may be removed from the substrate 100 to exposesource/drain regions 109 (FIG. 1D). In an embodiment, the portion of thefin structure 107 may be etched by a dry etch process to expose thesource/drain regions 109. In an embodiment, the source/drain regions 109may be etched to terminate on either the substrate 100 or the bottomwire (102 or 104). Optional undercut wet or dry etch processes can beutilized to remove additional materials in gate 108 region/tip overlaparea depending upon the particular device needs.

In an embodiment, silicon or silicon germanium source drain structures110 may be grown utilizing epitaxial growth techniques in thesource/drain regions 109 (FIG. 1E), and may be coupled to the portionsof the fin structures 107 disposed between the spacers 106. In anembodiment, the epitaxial source/drain structures 110 may be n-dopedsilicon for an NMOS device, or may be p-doped silicon/silicon germaniumfor a PMOS device, depending on the device type for the particularapplication. Doping may be introduced in the epitaxial process, byimplant, by plasma doping, by solid source doping or by other methods asare known in the art.

The tip and source/drain junction can be engineered by combiningepitaxial layers doped with different dopant species and concentration.For example, when silicon germanium source/drains are utilized to addstrain in a silicon channel for a PMOS devices, a silicon etch stoplayer/tip 112 may be grown first before the source/drain silicongermanium epitaxial structures 110 are grown, to avoid etching in thesource/drain regions 110 during a subsequent silicon germanium etch(FIG. 1F). In other words, the PMOS tip material needs to be resistantto a subsequent silicon germanium etch process.

An interlayer dielectric (ILD) may be formed on the substrate 100 (notshown) over the source/drain structures 110 and the gate 108 and spacers106. A top portion of the sacrificial poly gate 108 may be opened bychemical mechanical polish (CMP), in an embodiment. The sacrificial gateelectrode material 108 may then be removed from between the spacermaterials 106 (FIG. 1G). FIG. 1H depicts an interior view between thespacers 106, wherein the fin structure 107 is disposed in between thetwo spacers (only one shown). In an embodiment, the silicon layers 104,104′ may be selectively removed from the fin structure 107 to open up agap 111 between the silicon germanium channels 102, 102′ (FIG. 1I). Inan embodiment, the silicon layers 104, 104′ may be etched selectivelywith a wet etch that selectively removes the silicon 104, 104′ while notetching the silicon germanium nanowire structures 102, 102′. Such etchchemistries as aqueous hydroxide chemistries, including ammoniumhydroxide and potassium hydroxide, for example, may be utilized toselectively etch the silicon.

In another embodiment, the silicon germanium layers 102, 102′ may beselectively removed from the fin structure 107 and from sidewalls toopen a gap 113 between the silicon channel layers 104, 104′ (FIG. 1J).In an embodiment, the silicon germanium 102, 102′ may be etchedselectively with a wet etch that selectively removes the silicongermanium while not etching the silicon nanowire channels 104, 104′.Such etch chemistries as carboxylic acid/nitric acid/HF chemistry, andcitric acid/nitric acid/HF, for example, may be utilized to selectivelyetch the silicon germanium. Thus, either the silicon layers may beremoved from the fin structure 107 to form silicon germanium nanowires102,102′, or the silicon germanium layer may be removed from the finstructure 107 to form silicon channel nanowire 104, 104′ structures inthe channel region between the spacers 106, In an embodiment, bothsilicon and silicon germanium channel material may exist on the samewafer, in the same die, or on the same circuit, for example as NMOS Siand PMOS SiGe in an inverter structure. In an embodiment with NMOS Siand PMOS SiGe in the same circuit, the Si channel thickness (SiGeinterlayer) and SiGe channel thickness (Si interlayer) may be mutuallychosen to enhance circuit performance and/or circuit minimum operatingvoltage In an embodiment, the number of wires on different devices inthe same circuit may be changed through an etch process to enhancecircuit performance and/or circuit minimum operating voltage.

A gate dielectric material 115 may be formed to surround the channelregion between the spacers 106. In an embodiment, the gate dielectricmaterial 115 may comprise a high k gate electrode material, wherein thedielectric constant may comprise a value greater than about 4. In anembodiment, the gate dielectric material 115 may be formed conformallyall around the silicon nanowire structures 104, 104′ between the spacers106 (FIG. 1K). In another embodiment, the gate electrode material 115may be formed all around silicon germanium nanowire structures 102, 102′in between the spacers 106 (not shown).

A gate electrode material 117 may then be formed around the gatedielectric material 115 (FIG. 1l ). The gate electrode material 117 maycomprise metal gate electrode materials such as pure metal and alloys ofTi, W, Ta, Al, including nitrides such as TaN, TiN, and also includingalloys with rare earths, such as Er, Dy or noble metals such as Pt. Thegap 113 between the silicon nanowire structures 104, 104′ may be filledwith the gate electrode material 117. In another embodiment, the gap 111between the silicon germanium nanowire structures 102, 102′ may befilled with the gate electrode material 117 (not shown). In anembodiment, standard CMOS processing may be further performed on thesubstrate 100 to fabricate a CMOS device according to embodimentsherein.

In an embodiment, an NMOS and/or a PMOS device may be formed. FIG. 1mdepicts an NMOS device that may be formed (depicting a single siliconchannel), wherein a trench contact 119 couples to the source drainstructure 110, which may be silicon doped n+ in some cases, dependingupon the particular application. A silicon epitaxial tip 112, which maybe n-doped in some cases, and may be disposed between the source drainstructure 110 and the substrate 100. The gate electrode material 117 maysurround the silicon nanowire channel 104.

FIG. 1N depicts a PMOS device (depicting a single silicon channel 104)wherein a trench contact 119 couples to the source drain structure 110,which may be silicon germanium doped p+ in some cases, depending uponthe particular application. A silicon epitaxial tip/etch stop 120, whichmay be p-doped in some cases, may be disposed between the source drainstructure 110 and the substrate 100. The gate electrode material 117 maysurround the silicon channel 104, which may comprise a strained siliconchannel 104 in some cases.

In some cases, a device utilizing silicon germnaium channel structures(such as those depicted in FIG. 1I for example) may have an advantage bycomprising a high carrier mobility due to the silicon germaniumproperties. In an embodiment, a gate all around silicon germaniumchannel device process may be similar to the gate all around siliconchannel device processing, except that the epitaxial layer stack 120 maybe reversed, that is the silicon material 104 will be formed on thesubstrate initially, and the silicon germanium formed on the silicon.Since the silicon underlayer will be removed selective to the silicongermanium, the source/drain may comprise silicon germanium, and the etchstop under the sacrificial gate electrode material may comprise silicongermanium as well to avoid substrate etching.

Embodiments herein enable the fabrication of self-alignedgate-all-around (GAA) silicon and silicon germanium channel transistorstructures and devices. Nanowire channel devices exhibit lowersub-threshold leakage due to short channel effect (SCE) reduction.Implementation of GAA SiGe high mobility channel device, for examplesuppress SCE effects. (GAA) devices can maximize the electrostatic gatecontrol to the channel.

In an embodiment, devices fabricated according to the variousembodiments herein may be provided with enhanced substrate isolation.Referring to FIG. 2A, a bottom nanowire channel 202 that is disposed ona substrate 200 may comprise a shorted trigate with poor subfin leakage,in some instances. One solution may comprise forming the device on asilicon on insulator (SOI) substrate 201 (FIGS. 2B-2C), whereinsource/drain structures 210 and nanowire structures 204 are disposed onan insulator material 203, such as an oxide material 203, rather thanbeing disposed on a bulk silicon substrate 200 (as depicted in FIG. 2A).By using a SOI substrate 201, the bottom nanowire 204 geometry can bedefined by etching the bottom oxide after a silicon germanium etching ofthe nanowire fin structure (similar to the nanowire fin structure 107 ofFIG. 1B, for example) and before forming the gate electrode material(similar to the gate electrode material 117 of FIG. 1l , for example).

For example, FIG. 2D depicts etching the dielectric to form one nanowireand one trigate structure, while FIG. 2E depicts etching the dielectricto form a device comprising two nanowires. In another embodiment,enhanced substrate isolation may be achieved by forming fin spacers 211on the fin 207 sidewalls after the trench etch (FIG. 2F). Then a secondtrench etch 214 may be performed to expose a bottom fin area 216, andthe silicon portion of the bottom fin area 216 may be oxidized (FIG.2G). Thus, a bottom nanowire of the device may be disposed on an oxideto improve substrate isolation. In another embodiment, fin spacers 211may be formed on the fin 207 sidewalls after the trench etch and fill(FIG. 2H). The bottom silicon portion 216 of the fin 207 may be oxidizedafter the STI recess formation/oxide fill to enhance substrate isolation(FIG. 2I). Thus, a bottom nanowire of the device may be disposed on anoxide to improve substrate isolation.

In an embodiment, there may be a gap 311 in a spacer 306 left by theremoval of silicon regions of a nanowire stack 307 (FIG. 3A). Afteraddition of a gate, such as a metal gate structure (similar to the gatestructure 117 of FIG. 1L for example), the gap 311 may create a veryhigh-capacitance parasitic region between the subsequently formed gateand the source drain structure 310. In an embodiment, the potentialparasitic region may be avoided by utilizing an epitaxial oxide 302 forthe starting stack, rather than silicon (which may or may not require anorientation change on the silicon substrate 300) (FIG. 3B). In anembodiment, alternating layers of an epitaxial semiconductor material304 may be formed on an epitaxial oxide material 302 that may be formedon the substrate 300.

For example, a Gd2O3 can be grown epitaxially on (111) silicon, andsilicon germanium can then be grown on top of the Gd2O3 to build up amultilayer stack on the substrate that can be etched into fin structures307, that may be subsequently formed into silicon germanium wires. Inanother embodiment, cerium oxide may be grown on (111) silicon (oralternatively on (100) silicon) to form the multilayer stack. With anoxide/semiconductor/oxide stack there is the option to not etch,partially etch, or fully etch the oxide material 302, 302′ of the finstructure 307 (FIGS. 3C-3E, respectively). The no etch option (FIG. 3C)resolves the capacitance issue, but at the cost of poorer confinement;the partial etch option (FIG. 3D) improves the confinement but at thecost of some level of parasitic capacitance.

In another embodiment, the gap 311 in the spacers that is adjacent tothe fin structures (depicted in FIG. 3A) may be filled with a secondspacer 312 comprising spacer-like material 312 or a low-k material 312from the source/drain 310 side of the spacer 306 prior to epitaxialgrowth of the source.drain (FIG. 3F). For example, materials such as butnot limited to SiON, SiN, SiC, SiOBN, and low k oxides may comprise thesecond spacer 312 material. In one embodiment all of the silicon in theetch of the stack 307 may be removed, so that the replacement gate etch(removal of the sacrificial gate electrode material) only hits oxide. Inanother embodiment, only a portion of the silicon may be removed, sothat the replacement gate etch actually etches silicon. In anotherembodiment, the gap 311 may be filled from the gate side (prior to gatedeposition) with a spacer-like material 312 or a low-k material 312(FIG. 3G). Embodiments include performing a full etch or partial etchesof the stack 307 (shown as full etch).

In another embodiment, the gap 311 may be filled by exploiting theanisotropy of silicon etches to minimize the etch out of the siliconduring the removal step from the stack 307. For example, a (110) wafermay be used with a channel along <111>. This structure will haveslow-etching (111) planes facing the source/drain structures 310, thuslimiting undercut. The wet etch selected here must also etch SiGe moreslowly than Si, leaving a partially etched SiGe nanowire after removingall of the silicon between the SiGe nanowires. Thus, an anisotropic etchmay be used to minimize lateral etching inside the spacer 306, whereinthe etch chemistry is highly selective to silicon and not selective tosilicon germanium.

In an embodiment, vertical architecture scaling may be achievedutilizing nanowires. In an embodiment, silicon germanium or silicon maybe epitaxially grown from a substrate into a trench, and then oxidationor etching processes, for example, may be used to separate finstructures into nanowires, wherein the nanowires may be stackedvertically upon each other. In an embodiment, oxidation for the entirewire, wherein the source/drain region starts out as layers of SiGe (orSi) and oxide) may be performed. Alternating oxide 404 and nitridelayers 402 (more layers may be used to form more wires) may be formed ona silicon substrate 401 (FIG. 4A). The oxide and nitride layers may bepatterned and etched to form a trench 405 and a back portion 406,wherein the trench 405 exposes the silicon material of the substrate 401(FIG. 4B). Silicon germanium (or silicon) 407 may be grown epitaxiallyin the trench 405 and back portion, and may be polished (FIG. 4C). Ahard mask 408 may be formed on the silicon germanium (or silicon) 407,and maybe patterned and etched to expose sides of fins 410 (FIG. 4D). Inan embodiment, a fin structure may be formed by removing a portion ofthe alternating layers of nitride and oxide not covered by the hardmask.

The fins 410 may be oxidized to define nanowires (FIG. 4E). The oxidizedportions of the fins 410 may be removed to form the nanowires 412 whichmay serve as channel structures for a device, and may be formed acrosssubstantially the entire structure. In an embodiment, a first nanowire412 may be disposed vertically above a second nanowire 412′. In anotherembodiment, the wires may only be defined in a channel region (FIG.4G-4J). A second mask material 413, for example SiC, may be formedaround a fin structure 410. The second mask material 413 may beselective to oxide and nitride. The fin structure 410 may comprisealternating oxide/nitride films, similar to those in FIG. 4D, forexample. A trench 414 may be opened up to define a gate region adjacentto the fin structure 410, where a gate electrode material may besubsequently formed and wherein a portion of the fin structure 410 maybe exposed (FIG. 4H). Oxidation may be performed to define the nanowires(FIG. 4I), and the wires may be further defined by removing the oxidizedportions of the fin structure (FIG. 4J). Thus the wires are formed inthe gate region/trench 414, but not in the source/drain region.

To ease the lithography concerns of patterning the nanowires, a spacerprocess can be used. Here, side portions of the Si or SiGe fin 410 maybe exposed (while a top portion may be covered by a hard mask 421, suchas SiC, for example) by etching the nitride surrounding it and a spacer420 is formed by a combination of isotropic deposition and anisotropicetching (FIG. 4K). This spacer 420 is then used to mask the etch thatexposes the sidewalls of the fins 410. The spacer 420 could then beremoved.

In another embodiment, an anisotropic wet etching separates the finsinto wires as shown in FIG. 4I. First the oxide may be etched away usinga wet etch. Subsequently a wet Si or SiGe anistropic etch may be used toetch the exposed SiGe or Si of the fin 410. Because of the dependence ofthe etch rate on the crystal direction, the nanowires may be formed.After both etches are performed, the nanowires may be formed in ahexagonal shape, in an embodiment. Si or SiGe fins may be formed afterremoval of the oxide (FIG. 4M).

Vertical scaling of nanowires may be achieved. Since phonon scatteringmay limit the nanowire size to about 7 nm, this may limit the long termscaling of such devices. One solution is to construct the devicesvertically, with either the N or P channel located in a bottom wire andthe other channel located in a top wire. In an embodiment, an N+substrate may be used for Vss. In another embodiment, top and bottomcontacts may be misaligned. In another embodiment, wires with left andright wings may be formed. FIG. 5A depicts an inverter done with the N+substrate 500 for Vss and gate 501. Note that this needs a tall contact512 (TCN) to connect N and P nanowire channels 514, a short top TCN 510to couple with one of the N and P nanowire channels 514, and a substrateplug 508/bottom TCN coupled to one of the N and P nanowire channels 514and to the substrate 500. FIG. 5B depicts a misaligned top 510 andbottom 508 TCN. FIG. 5C depicts N and P nanowires in comprising left andright wing nanowire structures 514. FIG. 5D shows an inverter wired withthe left and right wing nanowire structures 514.

Nanowires with GAA offer improvement over GAA non-nanowire structures,as well as fins, and trigate structures. The use of lateral nanowireswith replacement metal-gate (RMG), gate-all-around processing is alogical extension of the roadmap from planar with RMG, to fins with RMG.Gate-all-around (GAA) nanowire structures offer the potential forimproved short channel control over GAA non-nanowire structures andfins. Improved Isolation of the bottom wire in a silicon or silicongermanium nanowire structure from the substrate may be achievedaccording to embodiments herein.

Density scaling when the smallest nanowire size is limited to >˜7 nm dueto phonon scattering may be enabled. Lateral nanowire structures forboth silicon and silicon germanium may be incorporated with replacementmetal-gate architecture and manufacturing-compatible fabricationtechniques for the wires modified from those developed for frigatestructures. Vertical architecture scaling with nanowires is enabled.Building circuits in the transistor layer itself using nanowires isenabled herein.

FIG. 6 shows a computer system according to an embodiment. System 600includes a processor 610, a memory device 620, a memory controller 630,a graphics controller 640, an input and output (I/O) controller 650, adisplay 652, a keyboard 654, a pointing device 656, and a peripheraldevice 658, all of which may be communicatively coupled to each otherthrough a bus 660, in some embodiments. Processor 610 may be a generalpurpose processor or an application specific integrated circuit (ASIC).I/O controller 650 may include a communication module for wired orwireless communication. Memory device 620 may be a dynamic random accessmemory (DRAM) device, a static random access memory (SRAM) device, aflash memory device, or a combination of these memory devices. Thus, insome embodiments, memory device 620 in system 600 does not have toinclude a DRAM device.

One or more of the components shown in system 600 may include one ormore nanowire devices of the various embodiments included herein. Forexample, processor 610, or memory device 620, or at least a portion ofI/O controller 650, or a combination of these components may include inan integrated circuit package that includes at least one embodiment ofthe structures herein.

These elements perform their conventional functions well known in theart. In particular, memory device 620 may be used in some cases toprovide long-term storage for the executable instructions for a methodfor forming structures in accordance with some embodiments, and in otherembodiments may be used to store on a shorter term basis the executableinstructions of a method for forming structures in accordance withembodiments during execution by processor 710. In addition, theinstructions may be stored, or otherwise associated with, machineaccessible mediums communicatively coupled with the system, such ascompact disk read only memories (CD-ROMs), digital versatile disks(DVDs), and floppy disks, carrier waves, and/or other propagatedsignals, for example. In one embodiment, memory device 620 may supplythe processor 610 with the executable instructions for execution.

System 600 may include computers (e.g., desktops, laptops, hand-helds,servers, Web appliances, routers, etc.), wireless communication devices(e.g., cellular phones, cordless phones, pagers, personal digitalassistants, etc.), computer-related peripherals (e.g., printers,scanners, monitors, etc.), entertainment devices (e.g., televisions,radios, stereos, tape and compact disc players, video cassetterecorders, camcorders, digital cameras, MP3 (Motion Picture ExpertsGroup, Audio Layer 3) players, video games, watches, etc.), and thelike.

Although the foregoing description has specified certain steps andmaterials that may be used in the embodiments, those skilled in the artwill appreciate that many modifications and substitutions may be made.Accordingly, it is intended that all such modifications, alterations,substitutions and additions be considered to fall within the spirit andscope of the embodiments as defined by the appended claims. In addition,it is appreciated that various microelectronic structures, such astransistor devices, are well known in the art. Therefore, the Figuresprovided herein illustrate only portions of an exemplary microelectronicstructure that pertains to the practice of the embodiments. Thus theembodiments are not limited to the structures described herein.

What is claimed is:
 1. An integrated circuit structure, comprising: asubstrate; a horizontal nanowire channel structure above the substrate,the horizontal nanowire channel structure having a bottommost surface,wherein the horizontal nanowire channel structure has a first endopposite a second end; a gate electrode surrounding the horizontalnanowire channel structure, wherein a portion of the gate electrode hasan uppermost surface above the horizontal nanowire channel structure,and wherein a second portion of a gate electrode is beneath thebottommost surface of the horizontal nanowire channel structure;sidewall spacers adjacent to the gate electrode, wherein a portion ofthe sidewall spacers is laterally adjacent to the first portion of thegate electrode above the horizontal nanowire channel structure, whereinthe sidewall spacers have a bottommost surface below the bottommostsurface of the horizontal nanowire channel structure, and wherein firstand second ends of the horizontal nanowire channel structure do notextend beyond the sidewall spacers; a semiconductor material beneath aportion of the horizontal nanowire channel structure beneath thesidewall spacers, the semiconductor material comprising a materialdifferent than the horizontal nanowire channel structure, wherein theportion of the horizontal nanowire channel structure beneath thesidewall spacers is directly on the semiconductor material; andsource/drain structures on either side of the horizontal nanowirechannel structure, wherein a portion of the source/drain structures islaterally adjacent to and in contact with the portion of the sidewallspacers laterally adjacent to the portion of the gate electrode abovethe horizontal nanowire channel structure, and the source/drainstructures are in contact with respective ones of the first and secondends of the horizontal nanowire channel structure, and wherein thesource/drain structures have a bottom surface below the bottommostsurface of the sidewall spacers.
 2. The integrated circuit structure ofclaim 1, wherein the horizontal nanowire channel structure comprises isa silicon horizontal nanowire channel structure.
 3. The integratedcircuit structure of claim 1, wherein the horizontal nanowire channelstructure is a silicon germanium horizontal nanowire channel structure.4. The integrated circuit structure of claim 1, wherein the gateelectrode comprises a gate dielectric material surrounding thehorizontal nanowire channel structure, and a metal gate surrounding thegate dielectric material.
 5. The integrated circuit structure of claim4, wherein the gate dielectric material comprises a high k gatedielectric material.
 6. The integrated circuit structure of claim 1,wherein the source/drain structures comprise epitaxial silicongermanium.
 7. The integrated circuit structure of claim 1, wherein thesubstrate is an SOI substrate.
 8. The integrated circuit structure ofclaim 1, wherein the substrate is a bulk silicon substrate.
 9. Theintegrated circuit structure of claim 1, further comprising: a firsttrench contact coupled to a first of the source/drain structures; and asecond trench contact coupled to a second of the source/drainstructures.
 10. The integrated circuit structure of claim 1, wherein thesource/drain structures comprise p+ doped silicon germanium, theintegrated circuit structure further comprising: silicon epitaxial tipsbetween the source/drain structures and the substrate.
 11. Theintegrated circuit structure of claim 1, wherein the source/drainstructures comprise n+ doped silicon, the integrated circuit structurefurther comprising: silicon epitaxial tips between the source/drainstructures and the substrate.
 12. An integrated circuit structure,comprising: a substrate; a horizontal silicon nanowire channel structureabove the substrate, the horizontal silicon nanowire channel structurehaving a bottommost surface, wherein the horizontal silicon nanowirechannel structure has a first end opposite a second end; a PMOS gateelectrode surrounding the horizontal silicon nanowire channel structure,wherein a portion of the PMOS gate electrode has an uppermost surfaceabove the horizontal silicon nanowire channel structure, and wherein asecond portion of the PMOS gate electrode is beneath the bottom surfaceof the nanowire channel; sidewall spacers adjacent to the PMOS gateelectrode, wherein a portion of the sidewall spacers is laterallyadjacent to the portion of the PMOS gate electrode above the horizontalsilicon nanowire channel structure, wherein the sidewall spacers have abottommost surface below the bottommost surface of the horizontalsilicon nanowire channel structure, and wherein first and second ends ofthe horizontal silicon nanowire channel structure do not extend beyondthe sidewall spacers; a semiconductor material beneath a portion of thehorizontal silicon nanowire channel structure beneath the sidewallspacers, the semiconductor material comprising a material different thanthe horizontal silicon nanowire channel structure, wherein the portionof the horizontal silicon nanowire channel structure beneath thesidewall spacers is directly on the semiconductor material; and p+ dopedsilicon germanium source/drain structures on either side of thehorizontal silicon nanowire channel structure, wherein a portion of thep+ doped silicon germanium source/drain structures is laterally adjacentto and in contact with the portion of the sidewall spacers laterallyadjacent to the portion of the PMOS gate electrode above the horizontalsilicon nanowire channel structure, and the p+ doped silicon germaniumsource/drain structures are in contact with respective ones of the firstand second ends of the horizontal silicon nanowire channel structure,and wherein the p+ doped silicon germanium source/drain structures havea bottom surface below a bottommost surface of the sidewall spacers. 13.The integrated circuit structure of claim 12, wherein the PMOS gateelectrode comprises a gate dielectric material surrounding thehorizontal silicon nanowire channel structure, and a metal gatesurrounding the gate dielectric material.
 14. The integrated circuitstructure of claim 13, wherein the gate dielectric material comprises ahigh k gate dielectric material.
 15. The integrated circuit structure ofclaim 12, wherein the p+ doped silicon germanium source/drain structuresare p+ doped epitaxial silicon germanium source/drain structures. 16.The integrated circuit structure of claim 12, wherein the substrate isan SOI substrate.
 17. The integrated circuit structure of claim 12,wherein the substrate is a bulk silicon substrate.
 18. The integratedcircuit structure of claim 12, further comprising: a first trenchcontact coupled to a first of the p+ doped silicon germaniumsource/drain structures; and a second trench contact coupled to a secondof the p+ doped silicon germanium source/drain structures.
 19. Theintegrated circuit structure of claim 12, further comprising: siliconepitaxial tips between the p+ doped silicon germanium source/drainstructures and the substrate.